1. Field of the Invention
This invention relates to a hose construction and more particularly to a hose construction in which relative movement between the layers thereof is minimized when the hose is connected to a swaged fitting. 2. Description of the Prior Art
It has been found that failure of high pressure thermoplastic hose assemblies employing swaged fittings usually occurs at or near the connection between the hose and the fitting. The reason for this type of failure can be attributed to the swaging process and the relative movement between the hose layers which occurs during this process. During swaging, the shell of the fitting moves longitudinally in the direction of the free hose. This longitudinal movement forces the hose layers to move relative to one another in the longitudinal direction causing a bunching of the reinforcement material at or near the end of the shell. This bunching lessens the tension applied by the reinforcement to the core tube at the point where bunching occurs. When the hose is subsequently pressurized, the core tube will expand until sufficient resistance is supplied by the reinforcement. Such expansion of the core tube results in a corresponding decrease in core tube wall thickness at the bunching point. Thus, upon pressurization, the hose will bulge at this point. When the pressure is released, the core tube exhibits a tendency to return to its initial relaxed state. Repeated pressurization of the hose causes the core tube to fatigue and allows the molecules in the core tube to orient in the longitudinal direction which decreases the strength of the hose to radially directed forces in the area where the reinforcement has bunched and results in eventual hose failure.
Various approaches have been taken to alleviate this problem of bunching of the reinforcement material. For example, the reinforcement can be chemically bonded to the core tube. This limits the amount of relative movement between the first reinforcement layer and the core tube but each additional layer of reinforcement material can move longitudinally relative to its adjacent reinforcement layer causing bunching of the succeeding reinforcement layers resulting in lessening of the tension applied by the succeeding layers. Such relative longitudinal movement between the reinforcement layers can be minimized by bonding the layers together, however, such bonding makes the resultant hose structure relatively inflexible and bulky.
Because hose assemblies using swaged fittings have a tendency to fail near the fitting due to bunching of the reinforcement material in this area during the swaging process, it has become desirable to develop a hose structure in which the reinforcement layers remain engaged to the core tube and to each other during the swaging process while retaining flexibility.